/Engine/Source/Runtime/Slate/Public/Framework/Application/SlateApplication.h
Register a new user with Slate. Normally this is unnecessary as Slate automatically adds a user entry if it gets input from a controller for that index. Might happen if the user allocates the virtual user.
[TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [FSlateUser](API\Runtime\Slate\Framework\Application\FSlateUser) > RegisterNewUser ( [FPlatformUserId](API\Runtime\Core\Misc\FPlatformUserId) PlatformUserId, bool bIsVirtual )